Current wrapping or banding machines (both automatic and semi-automatic) for groups of products consist basically of a table for the groups of products (which may be rotary or fixed) and a structure that mounts the film feed means. This mounting structure may (in the case of a rotary table) consist of a simple vertical column on which a film feed unit runs in both directions or (usually, in the case of a fixed table) it may be equipped with horizontal arms or prongs that rotate around the group of products.
The film feed means consist of a film roll rotatably mounted on a vertical shaft connected to a plate that forms part of a carriage that mounts the film feed means. In addition to the roll, there is a plurality of rollers, also vertical, connected to the plate and designed to guide the film and keep it stretched as it is fed towards the group of products.
Besides these elements, more and more banding machines are now equipped with motor-driven units for pre-stretching the wrapping film, especially when cold stretch film is used. Pre-stretching increases the stabilizing effect of the film and proportionally reduces the weight of the film on each banded group of products.
To correctly stretch the film being fed so that it does not slip on the rollers and so that, in particular, the width of the film band is not reduced (thus cancelling the film weight reducing effect), it is necessary to provide at least one pair of additional rollers, driven by independent motors so as to have different peripheral speeds, placed very close to each other and with the wrapping film making a very large angle round the two rollers.
This means that, in addition to the existing structure of the feed means, the film feed unit must be equipped with a large number of closely spaced rollers on the film feed carriage. As a result of this structure, it is often very difficult for the operator to load the film (when the roll finishes or the film breaks) because there is very little space between the rollers and there is the risk of the operator crushing his fingers when inserting the end of the film manually between the rollers.
In one solution devised by the manufacturers of these machines to overcome this problem, the carriage mounting the film roll and the pre-stretch and guide rollers is made using only one mounting bracket in such a way that the carriage is offset This structure partly solves the problem of loading the film between the rollers (one end of the rollers is free) but necessitates precise dimensioning of the only supporting part and considerable stiffening of the rollers (since there is only one supporting point) and hence greatly increases the costs of the machine and renders assembly more complex.
Another solution designed to solve the above mentioned problem was to divide the mounting carriage into two parts, a fixed part and a moving part, that can rotate about a horizontal or vertical pivot axis. In this way, the operator can load the film by turning the moving part and feeding the end of the film into the free area from the fixed part.
The disadvantage of the second solution is that the carriage is larger and heavier because it is divided into two and thus requires suitable lifting means and increases the production costs of the unit. Moreover, in this solution, the rollers must be placed further apart and the angles of the wrapping film round the rollers must be reduced, thus reducing the quality of the pre-stretching operation.